The present invention relates to a method for botting a tap hole in a wall of a shaft furnace with the aid of a botting gun mounted on a carrier arm which can pivot about a support column through the action of at least a first hydraulic actuating cylinder, the said botting gun comprising a chamber in which a piston slides, said piston being actuated by a second hydraulic actuating cylinder in order to eject a botting mass, via a frontal muzzle of the botting gun, into the tap hole while the botting gun is held in bearing contact against the wall of the furnace through the action of the first hydraulic actuating cylinder. The invention also relates to a botting machine for the implementation of this method.
It is known that the tap holes of a shaft furnace and, more particularly, of a blast furnace, are botted with a plugging-up, or botting mass. This botting mass is inserted into the tap hole under a very high pressure with the aid of a botting gun or clay gun, and it plugs up the tap hole upon hardening. the botting masses are generally based on clay with synthetic additives accelerating the hardening process. Because of the high pressure under which modern blast furnaces work and the properties of the botting masses currently used, very high botting pressures are required in order to plug up the tap holes.
Modern botting guns are designed to operate at a botting pressure which can reach 200.times.10.sup.5 Pa or more at the exit of the frontal muzzle. In order to be able to operate at such a botting pressure, a hydraulic working pressure of the order of 300.times.10.sup.5 Pa is used in current botting guns.
During the botting process, the tip of the botting gun's frontal muzzle is pressed against the wall of the furnace. In order to insure sealing and to prevent leakage between the wall of the furnace and the muzzle of the botting gun, it is necessary to maintain between 10% and 20% of the botting pressure as a minimum contact pressure between the wall of the furnace and the tip of the frontal muzzle. Of course is it also necessary to balance the reaction exerted by the botting mass on the botting gun as this reaction tends to move the botting gun away from the tap hole. This reaction is proportional to the botting pressure. Up until now, this has been carried out by subjecting the hydraulic actuating cylinder which actuates the carrier arm of the botting gun to the full working pressure of the hydraulic system throughout the entire botting process.
Although botting guns are designed to perform the botting under these high pressures, it should be pointed out that this maximum pressure is not exerted throughout the entire botting process. In fact, in the initial phase, when the tap hole offers little resistance to the botting mass, the pressure exerted in order to eject the mass through the muzzle into the tap hole is relatively low, on the order of 50.times.10.sup.5 Pa or less. This pressure increases progressively until at the end of the botting process it reaches values on the order of 200.times.10.sup.5 Pa. This means that if throughout the botting process, the botting gun is applied with a constant force such as is required to maintain its contact against the wall of the furnace at the end of the botting process, this force is, at the start of the botting operation, at least four times greater than the actual force required. In fact, given that the reaction exerted by the botting mass on the botting gun increases only in proportion to the botting pressure, the contact pressure between the wall of the furnace and the tip of the frontal muzzle is four times higher at the start of the botting process than at the end, when it is equivalent to the minimum pressure required in order to insure the sealing between the wall of the furnace and the tip of the frontal muzzle. This high contact pressure at the start of the process runs the risk of breaking or pushing in the bricks surrounding the tap hole, this being all the more so since the annular rim of the muzzle of the botting gun has a relative sharp edge.